In chemical vapor deposition (CVD) and similar processes, it may be advantageous to deliver the precursor reagent into a suitable reaction chamber, in a vapor form. The precursor is evaporated within an independent but adjacent evaporation chamber, and integrally transferred to the reaction chamber by suitable means. Inside the reaction chamber, these vapors are made to further react with heated, or ionized, chemical species and to deposit, or coat, surfaces with a thin layer (Thin Film) of material derived from these reactions. These Thin Films, depending on the nature of the material deposited, have applications in optics (i.e., anti-reflective coatings), electronics (i.e., data storage media), electrooptics (i.e., infrared detectors), mechanical (abrasion resistant coatings), electromechanics (piezoelectric and piezoresistive coatings), a and other general materials research and development areas. Particular examples of materials deposited in Thin Film form by CVD are ferroelectric materials (lead zirconate, barium strontium titanate), high temperature superconductor materials (ytrium-barium-copper oxide), dielectrics (diamond, silicon dioxide), conductors (copper, aluminum).
Among the methods of obtaining a precursor in a vapor form is that of sublimating a solid precursor material. In many instances, however, the sublimation temperature is very close to the decomposition temperature for that material, with the subsequent formation of byproducts in solid form, or which deposit as films of different structure and behavior than the originally sought for.
In other instances in which the precursor is in a liquid form, the vapors are generated by boiling the liquid and/or by passing a carrier gas through it, to carry the vapors down to the reactor. Again problems with prolonged exposure to boiling temperatures, which may be close to the decomposition temperature, arise all too often. Deposition rates are also limited to the vapor carrying capacity of the carrier gas.
A flash evaporator that provides increased temperature stability and control will be less prone to operative failures, and will provide greater consistency of results than known evaporators. Such an evaporator that besides providing a larger range of evaporation rates (thus increasing the film deposition rates), and is easy to maintain and inexpensively repaired, if necessary, will provide additional benefits. It is a purpose of the present invention to provide such an improved evaporator.
U.S. Pat. No. 5,204,314 of Kirlin (1993) provides a method of vaporizing a reagent for CVD reactors. Kirlin provides for a foraminous vaporization structure that may have some utility for the specific compounds disclosed, but is not directly comparable with the present invention. The method of Kirlin does not describe a device (or a method) that provides the advantages of the present invention, as described hereinbelow.